Half of Five is Four?

Date: 11/04/2004 at 12:54:40
From: Don
Subject: Half of five is four?
What's the only number system where half of five is four?

Date: 11/05/2004 at 12:15:10
From: Doctor Rick
Subject: Re: Half of five is four?
Hi, Don.
This is more of a riddle than a math problem. The answer is really
two "number systems"; one is the written-out English name of the
number. Can you see the other yet?
- Doctor Rick, The Math Forum
http://mathforum.org/dr.math/

Date: 11/05/2004 at 12:32:39
From: Don
Subject: Thank you (Half of five is four?)
Thank you for your help. I appreciate the clue to get the first part
which made it easy to get the second part on my own.